user
Explain what the big bang theory is. Output:
assistant
The Big Bang theory is the scientific explanation for the origin of the universe. It states that the universe began as a very dense and hot state roughly 13.8 billion years ago, and has since been expanding in size. It is the most widely accepted theory of the origin of the universe due to its explanation of diverse observations of the cosmos such as the cosmic microwave background radiation and the abundance of certain elements.